I am traumogenic (trauma created/clinical DID) plural system. It is highly likely that I never had a "core personality" that I was born as and instead have always had either an infant mental state or multiple personalities. (During the time most babies begin to form a coherent personality, I formed several. It is possible that not every system forms like this but highly like I did)
Every time I've felt I was singular, I've experienced mental walls, amnesia and other DID symptoms. If someone could do a "I'm singular ama" that'd be cool because I have questions too. :)
For the shit posting, we have an alter who thinks we should have learned calc and other higher maths by now. There is another alter in the system who used to compulsively read tumblr blogs that affirmed one of her identifies and the validity of a trauma we experienced. Others in the system got annoyed whereas others adapted their joking (shitposting but make it clinical) to the interests of this alter. She really wasn't getting that support irl, so that got her invested in these online communities. I think our system has been helped enough by mutual aid and screwed over enough by institutions (Paging Jennifer Freyd and her work on institutional betrayal) that the system views shitposting as a valid means of socializing.